A thermosiphon system uses a process of passive two-phase heat exchange that involves moving heat based on natural convection. Convection is the movement of fluid caused by heat. In particular, hotter fluid tends to rise compared to colder fluid because the hotter fluid is less dense than the colder fluid, which is influenced by gravity to sink. This physical effect results in a transfer of heat carried by the fluid without the need of a mechanical pump.
A thermosiphon system includes a pipe that contains the fluid (e.g., a high pressure refrigerant) used for heat exchange. The pipe provides passive two-phase transport of the fluid between a condenser region of the pipe and an evaporator region of the pipe. The evaporator region is physically located below the condenser region. Fluid in the condenser region condenses as it cools, and the condensed fluid flows from the condenser region to the evaporator region of the pipe due to gravitational and/or centripetal forces. In the evaporator region, the fluid is heated, which causes the fluid to evaporate. The evaporated fluid then flows from the evaporator region to the condenser region of the pipe via buoyancy forces. The fluid cycles through this two-phase process during heat exchange.
When using a thermosiphon system for two-phase passive heat transport, one problem that must be addressed is managing high heat-flux conditions in the evaporator region and/or in the condenser region of the pipe(s) forming the thermosiphon system. For example, increasing heat transfer in the condenser region (or likewise the evaporator region) of a pipe of a thermosiphon system without suffering the losses and/or ΔT increases (i.e., increase in temperature differential) imposed by the increasing heat-flux (amount of heat transferred per unit area per unit time) in the condenser region requires an increase in surface area in the condenser region (i.e., an increased surface area for heat transfer between the working fluid and the cooling mechanism, e.g., a thermoelectric cooler). Conventional solutions to this problem include using complicated heat exchangers or manifolds to increase the surface area for heat exchange. These solutions are generally cost-prohibitive. Moreover, the benefits of these solutions are further negated when using high pressure refrigerants because the walls of the container used for heat exchange must be thickened to safely contain the highly pressured refrigerant, which causes significant thermal conduction losses (i.e., impedes thermal conduction).
Accordingly, a need exists for mechanisms to achieve high heat transfer rates in a thermosiphon evaporator and/or condenser while mitigating the drawbacks caused by an increased heat-flux.